This invention relates to a wire cut electric discharge machining method in which electric discharge is caused to occur between a workpiece and a wire electrode through a machining solution.
FIG. 1 is an explanatory diagram showing the arrangement of an electric discharge machine. FIGS. 3A and 3B are a plan view for a description of a conventional wire cut electric discharge machining method.
In FIG. 1, reference numeral 1 designates a wire electrode; 2, a workpiece; 3, a table; 4, a wire guide section including a machining solution supplying section; 5, a machining contour along which the workpiece is cut; and 6, a robot for handling and removing a core (or product) cut off the workpiece. In FIG. 2, reference numeral 7 designates an upper nozzle; 8, a lower nozzle; and 9, a core cut off. In FIG. 3B, reference numeral 10 designates the remaining part of the workpiece; and 11, a machining groove.
The operation of the conventional electric discharge machine thus arranged will be described. Before an discharge machining operation is started, electric discharge machining conditions such as electrical conditions and machining speed are set. According to a predetermined program, the electric discharge machining operation is automatically carried out as follows:
The machining solution is applied between the wire electrode 1 and the workpiece 2 on the table 3 by the machining solution supplying section. Electric discharge is caused to take place between the wire electrode and the workpiece through the machining solution thus applied, to cut the workpiece along the contour 5. Upon completion of the discharge machining operation, the core 9 is cut off the workpiece, and held on the lower nozzle 8. Then, the core 9 is removed from the lower nozzle 8 with attracting means, such as an electromagnet, secured to the robot 6. Thereafter, at the next discharge machining point, the discharge machining operation is automatically carried out again in the same manner.
The automatic electric discharge machining of the workpiece 2 will be described in more detail. As shown in FIG. 3A, the machining operation is started at the machining starting hole Pl, and cutting the workpiece along the machining contour under the predetermined machining conditions is started at the point P2. That is, the wire electrode is moved clockwise as indicated by the arrow, and returned to the original point P2. In the discharge machining operation, the machining conditions are maintained unchanged. Thus, the workpiece has been cut along the machining contour.
As was described above, in the conventional wire cut electric discharge machining method, the electric discharge machining of a workpiece along a closed contour by moving the discharge machining point circularly (from the start position P2 to the same position P2) is carried out with the machining conditions maintained unchanged. Therefore, as the wire electrode 1 approaches the last point P2; that is, as the remaining part of the contour to be machined descreases, the core 9 may rock in the groove 11, for instance, because of the pressure of the machining solution as shown in FIG. 3B. Therefore, even when the wire electrode 1 has reached the last point P2, the core 9 is not completely cut off the workpiece with the remaining part 10 formed. The remaining part 10 must be manually cut. This will not only make the machining operation troublesome, but also adversely affect the machining accuracy of the cut surface. For the same reason, after the core 9 is cut off in this manner, the robot may become inoperable, so that the automatic discharge machining operation is suspended.
Furthermore in the above-described conventional method, since the discharge reaction acts on the machining part of the wire electrode 1 supported at two points above and below the workpiece 2, the wire electrode 1 is bent arcuately. Therefore, although the wire electrode has reached the predetermined final machining point, the core is not completely cut off the workpiece with the remaining part which must be manually cut later.